skidder

Got a picture of the vehicle with those tires?

The only steel grate bridge I remember crossing was in the San Francisco Bay area when I lived there a few decades ago. It was the one connecting Martinez to Benecia where the San Joaquin/Sacramento rivers come into the San Francisco/San Pablo Bay. Pretty unnerving the first times I did it as the distance down to the river is huge (just don't look down!). But as for flats I never had a problem on it and I used either 700x 28-32 tires or 26 x 1.5 on a street-converted mountain bike (from what I recall from those days). Usually had to slow down anyway since the winds coming across the bridge can get quite gusty.